Does a GFI actually trip on over current?

[eamarquardt]

I'm taking a break and sitting on the bench in the dugout.

Cheers,

Gus

[davefullmer]

Wow!

Hey guys, I'm almost sorry I asked the question about a GFI being able to act as a fuse.

This is all VERY interesting, I didn't expect this much explanation.

My biggest concern was that Mike unintentionally recommended using a GFI at the beginning of the TD circuit as a fuse and that by doing so, some folks who haven't even a working knowledge of electricity would use that advice and in reality would be inviting an fire to happen.

There are lots of us who understand how to wire homes and circuits without the specific physics involved in phase control, etc. I have been involved with electrical circuits in machine control since 1963 and what I don't know about electricity could fill several volumes of text books.

What I do know is that if someone wires a TD or any circuit and expects a GFI device to protect them current wise, there is a real potential for overloading the circuit and causing wires to heat up and melt. THIS CAUSES FIRES. And I sure would hate to see someone's camping fun end up this way.

As far as transmission by AC or DC, I don't have any experience with DC transmission lines so I will stay out of that debate. I do know that if Edison had had his way, rural electrification as we know it would never have happened because of the problems with transforming DC current up into the high voltages needed to keep the wire size small enough. In those days, the technology simply required high voltage and smaller current to maintain the wattage. Maybe nowadays, technology is there to switch DC to higher voltages for long distance transmission, but in Edison's days, solid state devices were a long way from being deveolped.

And with that said, I will shut up and just watch the debate. Probably will learn something to boot.

Dave

[Larwyn]

Dave,

Sorry to have participated in the hijacking of your thread. In answer to your original question; the instruction sheet that came with the GFCI outlet that I installed on the outside of my new shop last week stated that it is not an overcurrent device and the circuit must be protected by a properly sized fuse or circuit breaker.

I'm sure that the reason Mike suggested the GFCI was simply to provide ground fault protection and rely on the campground breaker for over current protection.

Personally I used both on my TD;

[Chuck Craven]

This is my personal thought on having a breaker panel in my camper.
My tear will be powered “AC” with a 20 amp cord from the power pole or outlet.
But most of the time it will be connected to a 15-amp outlet with a 20 to 15-amp adaptor. So an internal 20-amp breaker panel will never do any thing, the source outlet breaker or fuse will do the over current protection. I have only gone camping in only one place that there was not a breaker and GFI protection in the power pole for that campsite. It was a Ma and Pop camp ground from the 20’s that was never updated or very well maintained. I always check the plug that I will connecting to for proper safety ground, hot and neutral. The little power testers are cheep and easy to use. Just keep one in the camper all the time. My electrical panel has a place for it to be kept, ready for use. The AC power will mainly be used to charge the 12 dc battery and a 12-power supply to run all the 12 lights and appliances. The only other need for AC power, may be a crock-pot, frying pan or an Air Conditioner for very occasional use and never at the same time. I some times camp in campgrounds but most of the time it is primitive camping and with no excess to AC power. With this said there was one thing that was left out of our discussion.

There are some electrical codes that are written bye states and municipalities that states, you can’t have two equal breakers (current controlling devices) with an out bord sub panel, on the same single electrical circuit. So in this case your tear with an electrical breaker panel would not meet their code requirements. Remember any state or municipality can write electrical codes more stringent than the national codes. Would you be caught "NO" unless you start an electrical fire and some one got hurt.


It’s just some thing else to think about. Some times the simpler is better. (KISS)

Chuck

[davefullmer]

Nice neat looking job on your controls. \

And don't feel bad about any hijacking. I thought back on page 2 that all that needed to be said about GFI's had been said. All of this has been quite interesting to at least some of us.

Dave

[brian_bp]

I don't think that you would have to reverse the polarity when switching dc on and off on the primary side of the transformer. When you turned the dc on the primary field would expand cutting the windings of the secondary driving the current one way. When you switched the dc off, the primary field would collapse cutting the secondary winding and causing the electrons to flow in the opposite direction. Thus alternating current. There are many factors, I presume, that would be involved shaping the output wave form and I can guess what they might be but couldn't predict what the output would look like under any given circumstances.

Cheers,

Gus

Right... just switch a DC source on an off repeatedly and you get a square wave. Where it is relative to some zero reference fundamentally doesn't matter to a transformer.

The output is a series of pulses, one per current step (up and down), in alternating directions (polarities). It takes a bunch of conditioning to make that look anything like a sine wave. Mathematically, think of the output as the time derivative of the input current (which doesn't step nicely with the voltage since the transformer is not a simple resistive load)... or, reduce the pain in the head by skipping the math.

[prohandyman]

Dave wrote:

I thought back on page 2 that all that needed to be said about GFI's had been said

Ok Dave help me out.
Maiden voyage of tear this weekend. Have Shore power plug connected to a 50 amp breaker box, with just a 20 breaker installed. Power runs from there out to a outlet box with a GFCI outlet, then on to two other oulets. Have microwave plugged into one, nothing in the other two. I am a qualified (or so I thought electrician). As soon as I plug my extension cord into shore power plug, the GFCI breaker in both my garage and the camp site I used this weekend trips! I plugged the cord into a non-protected outlet and everything works. What could be tripping the GFCI?
Let me be clear - the GFCI in the garage and campsite trips - not the one in the camper. I bypassed my breaker box and plugged the cord directly into all appliances on board and everything works! Box is wired with hot to breaker, neutral and ground to neutral buss. Should the ground be elsewhere?

[Nitetimes]

And you guys are concerned with grounding your trailers....pfffftt!!!



I don't see any concern here!! Of course I do see quantities of alcohol!!

[Miriam C.]

I bypassed my breaker box and plugged the cord directly into all appliances on board and everything works! Box is wired with hot to breaker, neutral and ground to neutral buss. Should the ground be elsewhere?

I have my breaker box wired with a ground bar and a neutral bar (came in the box). I ran the ground to the ground bar only. The neutral goes to neutral bar only. If your breaker didn't come with a ground bar then you need one.

Inlet is wire with 3 prong so 3 screws. The ground comes through the shore power.

http://tnttt.com/viewtopic.php?t=20164

[davefullmer]

Dan,

I am not sure where your problem would be. It has been some months since I wired a GFCI outlet and I don't have one in my stock pile just now.

I am thinking that the problem could be because of plugging into a shoreline GFCI outlet, but until I get an outlet tomorrow and study it out a little, I just can't say for sure. What I have observed in the past is if you have a ground where you shouldn't have or if you don't have a ground where you should have it, the GFCI will trip. It will trip under both conditions.

Also, your final question about where the ground should be (in the breaker box) . The ground should be connected to neutral in the breaker box, but that could cause the shore line GFCI to trip (I'm thinking).

As you can see, I don't have the off the top of my head answers like some of these other experts, I have to study it out and actually make some tests when I am in doubt.

Actually, I hadn't thought before of the effects of plugging a GFCI circuit into another GFCI circuit. Now we should get all kinds of expert comments again.

I will let you know my observations. I am definitely going to look into this.

Dave

[Chuck Craven]

I bypassed my breaker box and plugged the cord directly into all appliances on board and everything works! Box is wired with hot to breaker, neutral and ground to neutral buss. Should the ground be elsewhere?

I have my breaker box wired with a ground bar and a neutral bar (came in the box). I ran the ground to the ground bar only. The neutral goes to neutral bar only. If your breaker didn't come with a ground bar then you need one.

Inlet is wire with 3 prong so 3 screws. The ground comes through the shore power.

http://tnttt.com/viewtopic.php?t=20164

Do not connect the green safety ground to the white neutral.
That will make your extinction cord from the power plug or campground power pole in to a transformer. This can fake out the GFCI circuit you plug into as an uneven load current draw. The hot wire current will be different than the return current, which will come back part on the neutral wire and part on the safety ground wire. The source GFCI breaker or outlet will disable the AC power to all loads. That is what it is spouse to do.


Chuck

[prohandyman]

Makes perfect sense! I guess I wired it the same day that I cut my thumb off - wasn't thinking then either!

[Larwyn]

Actually it is quite simple, the neutral should only be bonded to ground at one point. The ground and neutral should be seperate and isolated in the TD breaker box, as they should be grounded in the campground box. This is the main cause of faulse trips on circuits feed from sub panels (such as the breaker box in the TD) on GFCI circuits.

[davefullmer]

Thanks Larwyn,

That's what I was thinking also. By plugging the shore line into a GFIC, his grounding connecting the neutral to the ground wire in his TD breaker box was tripping the shore line GFCI.

I really can't see any sense in trying to have 2 GFCI's in series anyway.

Dave

[prohandyman]

Dave wrote:

I really can't see any sense in trying to have 2 GFCI's in series anyway

Dave
I wanted a GFCI in the tear in case I hooked up to power that did not have one. I guess I didn't expect the campground box to have one also! Is that common, and if so, I might take mine out!